The present invention relates to a switched-capacitor-type stabilized power unit.
FIG. 19 shows a structure of a switched-capacitor-type stabilized power unit 101 for obtaining an output voltage twice as much as an input voltage. The stabilized power unit 101 is structured so as to include an integrated portion 101a, and a voltage-increasing capacitor C101, an input capacitor C102, an output capacitor C103, and voltage-dividing resistors R101 and R102 provided outside the integrated portion 101a. The integrated portion 101a is provided with switches S101, S102, S103, S104, a control section 111, a comparator 112, and a reference voltage source 113. Further, the integrated portion 101a is provided with an output terminal T101 outputting an output voltage Vo, an input terminal T102 to which an input voltage Vin is inputted from a power source such as a battery, a feedback terminal T103 for the output voltage Vo, a GND terminal T104, a capacitor connection terminal T105 to which an electrode Cxe2x88x92 having a lower potential of the voltage-increasing capacitor C101 is connected, and a capacitor connection terminal T106 to which an electrode C+ having a higher potential of the voltage-increasing capacitor C101 is connected.
In the stabilized power unit 101, a switched capacitor section is structured by the switches S101, S102, S103, S104, and the voltage-increasing capacitor C101. The control section 111 controls switching operation of the switches S101, S102, S103, S104 in the switched capacitor section. When the control section 111 controls the switches S101 and S103 to be ON and the switches S102 and S104 to be OFF, and the input voltage Vin is applied to the input terminal T102 via the input capacitor C102, the voltage-increasing capacitor C101 is charged. Next, when the control section 111 controls the switches S101 and S103 to be OFF and the switches S102 and S104 to be ON, the respective potentials of the electrodes of the voltage-increasing capacitor C101 increase by the potential of the input terminal T102. The voltage increased by such an operation is outputted as the output voltage Vo via the output capacitor C103.
The output voltage Vo is detected by the voltage-dividing resistors R101 and R102, and a voltage Vfb101 at a point connecting the voltage-dividing resistors R101 and R102 is inputted to a non-reversal input terminal of the comparator 112. The comparator 112 compares the voltage Vfb101 with a reference voltage Vref101 generated by the reference power source 113 and inputted to a reversal input terminal. When the voltage Vfb101 reaches the reference voltage Vref101, the comparator 112 outputs a signal to the control section 111 so as to stop the switching operation of the switches S101, S102, S103, S104. The comparator 112 is a comparator having a hysteresis function, and when the switching operation is stopped and the output voltage Vo decreases, that is, the voltage Vfb101 decreases, the comparator 112 outputs a signal to the control section 111 so as to resume the switching operation of the switches S101, S102, S103, S104. By repeating the foregoing operation, the stabilized power unit 101 stabilizes the output voltage Vo.
FIG. 20 shows a time chart on the operation of stabilizing the output voltage Vo in the stabilized power unit 101. At time t0, the switches S101 and S103 are ON and the switches S102 and S104 are OFF, and the input voltage Vin is started to be applied, the voltage-increasing capacitor C101 becomes charged, and the potential of the electrode C+ of the voltage-increasing capacitor C101 becomes Vin. Next, at time t1, the switches S101 and S103 are OFF and the switches S102 and S104 are ON, and the potential of the electrode C+ of the voltage-increasing capacitor C101 becomes 2Vin, a charge to the output capacitor C103 is started, and the output voltage Vo comes to be increased. At time t2, the respective switches are in the conditions identical to those at the time t0, and the potential of the electrode C+ of the voltage-increasing capacitor C101 becomes Vin again. At time t3, the respective switches are in the conditions identical to those at the time t1, and the potential of the electrode C+ of the voltage-increasing capacitor C101 becomes 2Vin, and the output capacitor C103 becomes charged. In a period from the time t2 to the time t3, since an output current flows from the stabilized power unit 101 to a load, a discharge from the output capacitor C103 is carried out, and the output voltage Vo is decreased.
The output voltage Vo is increased by repeating such a charge and a discharge to and from the output capacitor C103 in a predetermined duty. When the output voltage Vo reaches a predetermined threshold level COM1, that is, when the voltage Vfb101 at the point connecting the voltage-dividing resistors R101 and R102 reaches the reference voltage Vref101, the comparator 112 outputs a signal for stopping the switching operation to the control section 111. Suppose that this occurs at time tk, the switches S101 and S103 are ON and the switches S102 and S104 are OFF at the time tk, and the condition is maintained. After the time tk, the output voltage Vo continues to be decreased until it declines to a predetermined threshold level COM2, where the comparator 112 outputs a signal for starting the switching operation to the control section 111. Suppose that this occurs at time tn, the switches S101 and S103 are OFF and the switches S102 and S104 are ON at the time tn, and the switching operation is started. In such a manner, the stabilized power unit 101 shifts from start-up state to steady state.
However, in the foregoing conventional stabilized power unit 101, when the output voltage Vo increases very steeply, there is a possibility that the output voltage Vo might overshoot and some load connected to the stabilized power unit 101 might fail to function properly.
It is therefore an object of the present invention to provide a switched-capacitor-type stabilized power unit which can prevent an overshoot of an output voltage at start-up, in a structure having an output capacitor which outputs a charged voltage obtained through a plurality of charges by switching operation utilizing a voltage-increasing potential of a voltage-increasing capacitor at the start-up, as the output voltage.
To achieve the foregoing object, a stabilized power unit of the present invention is a switched-capacitor-type stabilized power unit structured so as to include:
an voltage-increasing capacitor which is charged based on an input voltage and whose voltage is increased after being charged;
switching section for carrying out switching operation to alternately switch a charge period and a voltage-increasing period of the voltage-increasing capacitor; and
an output capacitor which outputs a charged voltage obtained by being charged utilizing a voltage-increasing potential of the voltage-increasing capacitor in the voltage-increasing period, as an output voltage, and stabilizes the charged voltage within a range of the output voltage in steady state through a plurality of the voltage-increasing periods after a start-up is started,
wherein the stabilized power unit includes soft start means for controlling the switching section to carry out the switching operation so that the charged voltage always becomes not more than the output voltage in the steady state, at the start-up from when the start-up is started until when the charged voltage is stabilized within the range of the output voltage in the steady state.
According to the foregoing invention, at the start-up, the soft start means controls the switching section to carry out the switching operation so that the charged voltage of the output capacitor always becomes not more than the output voltage in the steady state. With this structure, the charged voltage of the output capacitor becomes stabilized within the range of the output voltage in the steady state, without having an overshoot until the completion of the start-up. Consequently, it becomes possible to provide a switched-capacitor-type stabilized power unit which can prevent an overshoot of the output voltage at the start-up, in the structure having the output capacitor which outputs the charged voltage obtained through a plurality of charges by the switching operation utilizing a voltage-increasing potential of the voltage-increasing capacitor, as an output voltage.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.